Headlamp washers
Pole Position
Joined: Apr 2018
Posts: 2,626
Likes: 459
From: GA
So the European law requirement for headlight washers is simplistically mandating that all hi-power beams (e.g. Xenon) must have washing systems. The actual reasoning behind is more complex and it is based on research and engineering feedback. Some users above here have come close to the point but basically the reasoning is this:
The high-power discharge lamps (Xenon or strong halogens) both release high heat and also focus all the beam into a small area.
In the winter, the heat is normally sufficient that is melts the snow off the headlights (except in severe blizzards) so the washers are not needed. More so, if the snow is too thick and fluffy, the jets will simply be absorbed (think to a similar case similar to...he he..."golden snow") so again will not work. Then, in very low temperatures (around -40 C), most probably that the spray would rapidly freeze anyways so again no effectiveness. So to summarize, the headlight washers are not targeting the winter environment, but more the rainy-muddy autumn-spring ones, where you have a lot of dirt projected to the headlights, and due to the high localized heating from the beam, it drys out (lower temperature headlights with less heat remain humid and give a chance to humid dirt to smear off), so it continuously builds up dirt and completely obscures the headlight glass. This has two basic effects: on short-term, it seriously affects the visibility, which is a hazardous case for the drivers, and on long-term it strongly affects the bulbs and headlight assembly reliability, as it seriously decreases their lifetime due to higher temperatures than designed.
As for the LEDs, they are also generating less heat and are also more distributed to the headlight area so normally they behave thermally like older low-power bulbs, remaining humid so it is not that critical to use headlight washers for LED headlights. I think that in this case it is more of a "got-used-to" feature which remained as standard in some cases, or simply has been deleted in others.
The high-power discharge lamps (Xenon or strong halogens) both release high heat and also focus all the beam into a small area.
In the winter, the heat is normally sufficient that is melts the snow off the headlights (except in severe blizzards) so the washers are not needed. More so, if the snow is too thick and fluffy, the jets will simply be absorbed (think to a similar case similar to...he he..."golden snow") so again will not work. Then, in very low temperatures (around -40 C), most probably that the spray would rapidly freeze anyways so again no effectiveness. So to summarize, the headlight washers are not targeting the winter environment, but more the rainy-muddy autumn-spring ones, where you have a lot of dirt projected to the headlights, and due to the high localized heating from the beam, it drys out (lower temperature headlights with less heat remain humid and give a chance to humid dirt to smear off), so it continuously builds up dirt and completely obscures the headlight glass. This has two basic effects: on short-term, it seriously affects the visibility, which is a hazardous case for the drivers, and on long-term it strongly affects the bulbs and headlight assembly reliability, as it seriously decreases their lifetime due to higher temperatures than designed.
As for the LEDs, they are also generating less heat and are also more distributed to the headlight area so normally they behave thermally like older low-power bulbs, remaining humid so it is not that critical to use headlight washers for LED headlights. I think that in this case it is more of a "got-used-to" feature which remained as standard in some cases, or simply has been deleted in others.
Lead Lap
Joined: Jan 2004
Posts: 3,595
Likes: 271
From: Kansas
I suppose it depends on where you live and the condition of the roads you drive on. We've had a number of vehicles with headlamp washers and my experience has been different. I've found headlamp washers to be most important during the winter months when road grime from the substances used on icy/snowy roads (salt, sand, cinders) combines with the melting ice/snow and is kicked up by the wheels of other vehicles. It's not as much of an issue now that my wife and I are both retired and can do more of the driving on our frequent 200 to 350 mile winter trips during daylight hours.
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